It has been established that composite radiation-sensitive grains formed by the controlled site deposition of silver salt onto host silver halide grains having predominantly {111} crystal faces is capable of improving the photographic performance properties of the emulsion, as illustrated by Maskasky U.S. Pat. Nos. 4,435,501, 4,463,087 and 4,471,050 (hereinafter collectively referred to as the Maskasky salt deposition patents).
The Maskasky salt deposition patents demonstrate that advantageous photographic properties are realized when a site director is employed to direct silver salt deposition preferentially toward the edges and/or corners of the host grains. The Maskasky salt deposition patents demonstrate that high levels of iodide ion in the crystal lattice structure of the host grains or lower levels of iodide ion adsorbed to the host grains are capable of directing silver salt epitaxy. The Maskasky salt deposition patents also demonstrate that adsorbed organic compounds, such as J-aggregating spectral sensitizing dyes and aminoazaindenes (e.g., adenine), are also useful site directors for silver salt epitaxy.